But what mathematical property encapsulates ability to optimize by gradient descent for landscapes, such as in Fig. REF .
It turns out that a simple condition proposed in 1963 by Polyak [1]} is sufficient for efficient minimization by gradient descent. This PL-condition
(for Polyak and also Łojasiewicz, who independently analyzed a more general version of the condition in a different context [2]}) is a simple first order inequality applicable to a broad range of optimization problems [3]}.
